HELP !!! WD Caviar GP WD5000AACS 500 GB 3.5

The drive suddenly stopped showing up, or would freeze my computer, i guess itd go to sleep mode, or itd would just stop spinning, i took it out of the enclosure hoping it was an issue with the enclosure but it actually wasnt, the last few days ive been plugging it to the computer and it starts spinning fine and , im able to browse thru the data all good but then it just crashes it just stops and disappears , and once that i try to plug it again it does not start spinning again, until i wait a few hours.

Any suggestions !! what u think it can be ?